diff options
Diffstat (limited to 'device')
| -rw-r--r-- | device/peer.go | 25 | ||||
| -rw-r--r-- | device/peer_test.go | 29 |
2 files changed, 45 insertions, 9 deletions
diff --git a/device/peer.go b/device/peer.go index 8a8224c..65581d5 100644 --- a/device/peer.go +++ b/device/peer.go @@ -19,20 +19,27 @@ const ( ) type Peer struct { - isRunning AtomicBool - sync.RWMutex // Mostly protects endpoint, but is generally taken whenever we modify peer - keypairs Keypairs - handshake Handshake - device *Device - endpoint Endpoint - persistentKeepaliveInterval uint16 - - // This must be 64-bit aligned, so make sure the above members come out to even alignment and pad accordingly + // These fields are accessed with atomic operations, which must be + // 64-bit aligned even on 32-bit platforms. Go guarantees that an + // allocated struct will be 64-bit aligned. So we place + // atomically-accessed fields up front, so that they can share in + // this alignment before smaller fields throw it off. stats struct { txBytes uint64 // bytes send to peer (endpoint) rxBytes uint64 // bytes received from peer lastHandshakeNano int64 // nano seconds since epoch } + // This field is only 32 bits wide, but is still aligned to 64 + // bits. Don't place other atomic fields after this one. + isRunning AtomicBool + + // Mostly protects endpoint, but is generally taken whenever we modify peer + sync.RWMutex + keypairs Keypairs + handshake Handshake + device *Device + endpoint Endpoint + persistentKeepaliveInterval uint16 timers struct { retransmitHandshake *Timer diff --git a/device/peer_test.go b/device/peer_test.go new file mode 100644 index 0000000..de87ab6 --- /dev/null +++ b/device/peer_test.go @@ -0,0 +1,29 @@ +/* SPDX-License-Identifier: MIT + * + * Copyright (C) 2017-2019 WireGuard LLC. All Rights Reserved. + */ + +package device + +import ( + "testing" + "unsafe" +) + +func checkAlignment(t *testing.T, name string, offset uintptr) { + t.Helper() + if offset%8 != 0 { + t.Errorf("offset of %q within struct is %d bytes, which does not align to 64-bit word boundaries (missing %d bytes). Atomic operations will crash on 32-bit systems.", name, offset, 8-(offset%8)) + } +} + +// TestPeerAlignment checks that atomically-accessed fields are +// aligned to 64-bit boundaries, as required by the atomic package. +// +// Unfortunately, violating this rule on 32-bit platforms results in a +// hard segfault at runtime. +func TestPeerAlignment(t *testing.T) { + var p Peer + checkAlignment(t, "Peer.stats", unsafe.Offsetof(p.stats)) + checkAlignment(t, "Peer.isRunning", unsafe.Offsetof(p.isRunning)) +} |